Icecap may hold clue to dramatic climate upheavals

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The vaulting heap of ice that is the Greenland Icecap and the swirling seas nearby have emerged as vital pieces of a puzzle posed by global warming. Can the continuing slow increase in worldwide temperatures touch off abrupt climate upheavals?

Each piece of the puzzle is a dynamic and complicated body of water. Firstly, the North Atlantic here is about three kilometres deep and liquid; then the icecap is three kilometres high and solid. For scale, think of it as a freshwater Gulf of Mexico that has been frozen, inverted and plonked on top of a gigantic island.

Experts say the ice and waters here are in a state of profound flux. If the trends persist, they could mean higher sea levels and widespread coastal flooding, and perhaps a sharp cooling in parts of the northern hemisphere.

Although nobody expects shifts as cataclysmic as portrayed in the new movie The Day After Tomorrow, the cooling could disrupt the relatively stable climatic conditions in which modern human societies have evolved.

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In the past few years Greenland's melting zone had expanded to elevations almost two kilometres high in some places, said Konrad Steffen, a University of Colorado glaciologist.

Recent measurements by NASA scientists show that such melting can have dramatic effects on the ice sheet, with melted water percolating thousands of metres down through fissures and allowing the ice to slide more easily over the bedrock below, accelerating its march to the sea.

The influx of fresh water could block North Atlantic currents that help moderate the weather of the northern hemisphere.

Oceanographers say global warming may already be pushing the North Atlantic towards instability. In less than 50 years waters deep in the North Atlantic and Arctic have become significantly fresher, matched by growing saltiness in the tropical Atlantic.

In past millenniums when such oceanic breakdowns occurred, the climate across much of the northern hemisphere changed dramatically, with deep chills and abrupt shifts in patterns of precipitation and drought from Europe to Venezuela.

It is unclear whether the new melting will result in something similar. Gaps in understanding are enormous, but Greenland is being measured and monitored as never before, by satellite, aircraft and scientists braving 30-below-zero temperatures.

A US oceanographer, Ruth Curry, late last year reported a 40-year trend towards a freshening of the North Atlantic and growing saltiness in the tropics. The Atlantic was being pushed towards "a precipice" in three decades and a Greenland meltdown could push it over the edge, she said.

Some say the system could be self-regulating, with the shutdown of warm currents, in turn, cooling Greenland and stopping the melting. Another wild card is that further warming will increase snowfall and add as much frozen water to Greenland as is lost through melting or the splitting off of icebergs.

A snow hydrologist, Joseph McConnell, recently completed a three-week 400 kilometre snowmobile crossing of the ice sheet on Greenland, extracting shaft-like ice cores that will be analysed for shifts in dust types or subtle chemical markers. "If Greenland melted it would raise sea levels by six metres," he said. "There goes Florida; there goes most of the Mississippi embayment; there go the islands in the South Pacific. Bangladesh is obliterated. Manhattan would have to put up dykes."